To protect chum salmon eggs from water mold infection during incubation, the eggs were treated daily with sodium hypochlorite solution (NaOCl) at 10 mg/L residual chlorine concentration for 15 min during their developmental period from fertilization to eyed stages. The number of infected eggs and number of eyed eggs were observed on day 23 of incubation. The percentage of infected eggs to total eggs was significantly lower with NaOCl treatment (1.8 : 33.4%) than in the control (11.3 : 59.3%, P < 0.01). The percentage of eyed eggs to total eggs was significantly higher with NaOCl (85.9 : 98.6%) than in the control (66.1 : 97.5%, P < 0.01). The antifungal activity of NaOCl resulted in improving egg survival. Accordingly, NaOCl is a useful antifungal agent against water mold infection on chum salmon eggs.KEY WORDS: antifungal agent, chum salmon, fish egg, sodium hypochlorite, water mold.

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The anti-microbial activity of galangal (Alpinia galanga Linn.) is well known. In this study, the feeding of galangal crude extract was investigated for its effect on preventing the infectious diseases Vibrio harveyi and white spot syndrome virus in Pacific white shrimp (Litopenaeus vannamei). A commercial diet mixed with galangal ethanol extract was fed to shrimp for 1 or 2 months. In the first month of feeding, the growth rate of the galangal extract diet group was lowered compared with that of the control diet group, possibly because the shrimp required time to acclimatize to the galangal diet. After 2-months of feeding, the growth of the shrimp in terms of body weight, specific growth rate and survival rate of the galangal diet group did not differ significantly (P > 0.05) from that of the control diet group. The clearance ability was evaluated by counting the bacterial cells in the hemolymph of shrimp injected with V. harveyi in the abdomenal segment. The number of V. harveyi in the hemolymph of the galangal diet group was significantly lower than that in the control diet group (P < 0.05), indicating the higher clearance ability of the galangal diet group. The oral administration of galangal extract enhanced the resistance of Pacific white shrimp against V. harveyi and white spot syndrome diseases, as demonstrated by the significantly higher survival rate of the galangal diet group. These results suggested that galangal is useful as an alternative to chemotherapeutic treatment to solve the problems created by residual antibiotics in shrimp.

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